RNAIII inhibiting peptide (RIP), a global inhibitor of Staphylococcus aureus pathogenesis: structure and function analysis

Staphylococcus aureus are gram-positive bacteria that can cause serious diseases in humans and animals. S. aureus infections can be prevented by the heptapeptide RNAIII inhibiting peptide (RIP). RIP was originally isolated from culture supernatants of coagulase negative staphylococci presumed to be S. xylosus. The sequence of RIP was identified as YSPXTNF. Native RIP and its synthetic analogue YSPWTNF have been shown to be effective inhibitors of diseases caused by various strains of S. aureus, including, cellulitis, keratitis, septic arthritis, osteomylitis and mastitis. RIP is therefore considered to be a global inhibitor of S. aureus. We show here that: 1) the amide form of RIP (YSPWTNF-NH2) is highly stable and is therefore the one recommended for use. 2) RIP inhibits S. aureus pathogenesis by inhibiting the synthesis of both agr transcripts RNAII and RNAIII. 3) Although RIP inhibits agr, it also reduces bacterial adherence to mammalian cells and to plastic (tested on HEp2 cells and on polystyrene by fluorescence and atomic force microscopy), suggesting that RIP can be used safely as a therapeutic molecule. 4) RIP derivatives were designed and tested for their ability to inhibit RNAIII in vitro and cellulitis in vivo. Not all peptides that inhibited RNAIII also inhibited an infection in vivo, indicating that studies must be carried out in vivo before considering a peptide to be of therapeutic potential. 5) The RIP derivative containing Lysine and Isoleucine at positions 2 and 4, respectively, inhibited S. aureus infections in vivo (tested on cellulitis), suggesting that both RIP YSPWTNF and its derivative YKPITNF are effective inhibitors of infections caused by S. aureus.